1. Field of the Invention
The present invention concerns an antenna selector switch to operate a number of antenna units of a magnetic resonance apparatus via an RF channel. The invention also concerns a method to switch between at least two antenna units.
2. Description of the Prior Art
Magnetic resonance is a known modality to, among other things, acquire images of the inside of a body of an examination subject. In a magnetic resonance (MR) apparatus rapidly switched gradient fields are superimposed on a static basic magnetic field B0 that is generated by a basic field magnet. To excite MR signals, the MR apparatus also has a whole-body radio frequency (RF) antenna that radiates RF signals (known as the B1 field) into the examination subject. The excited magnetic resonance signals can be acquired by the same antenna that was used to radiate, or with a different antenna such as a local antenna. The received signals are processed to form an image.
Antenna arrays are typically used in MR tomography. An antenna array has a number of individual coil elements. In newer imaging methods, for example in parallel imaging, the raw data respectively received by a number of coil elements are processed into MR images. In such methods the raw data of each coil element are separately conducted from the antenna array into a plug of the antenna array and supplied to the reception channels via this plug.
An example for an antenna array is a spinal column surface unit, also called a spine array. In such an antenna array with, for example, 24 coil elements, 12 coil elements, for example, cover the maximum acquisition volume (field of view FOV). This array thus requires at least twelve channels at the plug that are to be connected with twelve reception channels.
Particular coil elements that are not necessary for a given examination are detuned with regard to their resonance frequency with detuning circuits. The activation of such a detuning circuit for a coil element typically occupies a control signal line in the plug of the antenna unit. In conventional detuning circuits, a certain forward current typically is provided by the MR apparatus in the detuned state (inactivate state) to a PIN diode. In the active case, i.e. without detuning, a certain blocking voltage is applied to the PIN diode.
Unnecessary antennas are switched to the inactive state by the detuning circuits. For example, receiving antennas are switched to be inactive during the transmission mode and transmitting antennas are switched to be inactive during the reception mode. In addition to transmission using a whole-body antenna mentioned above, a B1 magnetic field can be radiated with good spatial localization by a local antenna array.
A problem in the use of raw data from a number of coil elements is the limited space for channels and control signal lines in the plug of the antenna array, which limits the number of the reception channels and the number of the control signal lines that can be available.